JP2008025706A - Hydraulic control circuit for working machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic control circuit for working machines whose usability is excellent in a simple structure, and whose energy efficiency is high. <P>SOLUTION: This hydraulic control circuit includes: a variable delivery pump 7; a regenerative circuit 23 which branches out from an oil passage between the exhaust side of a boom cylinder 1 operated by a hydraulic fluid supplied from the pump 7 through a boom control valve 5, and a flow control valve 10 changing the amount of flow of the exhaust side, and which communicates with the discharge side of the pump; a pressure sensor 15 which senses the pressure of the exhaust side of the boom cylinder 1; a pressure sensor 16 which senses the discharge pressure of the pump 7; a controller 8 which controls the flow control valve 9, 10, so as to perform regeneration returning the hydraulic fluid of the exhaust side to the pump discharge side through the regeneration circuit 23 when the pressure of the exhaust side of a boom cylinder 1 is higher than the pump discharge pressure, and which controls the pump 7 so as to decrease the amount of regenerative flow from the target amount of pump delivery flow set for no regeneration performed when this regeneration is performed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hydraulic control circuit for a working machine such as a hydraulic excavator.

  Conventionally, in a hydraulic work machine, potential energy and inertial energy are not regenerated but are converted into heat energy by a throttle and discarded, which has a problem of poor energy efficiency.

On the other hand, for example, in the technique of Patent Document 1, a variable displacement motor is coupled to the output shaft of the engine, and hydraulic energy of the actuator is regenerated by this motor. Further, in the technique of Patent Document 2, when a boom lowering operation is performed with a boom cylinder, the return oil is communicated with the control system of another actuator that uses a pump common to the boom cylinder through the expansion regeneration valve. However, this technique does not necessarily improve energy efficiency. Furthermore, in the technique of Patent Document 3, energy is saved by regenerating hydraulic oil discharged from the actuator and reducing the discharge flow rate of the hydraulic pump in accordance with the regenerative flow rate.
JP 2003-120616 A JP 2003-120604 A JP 2004-84907 A

  In the technique of the above-mentioned Patent Document 1, it is necessary to newly connect a variable capacity motor to the output shaft of the engine, and there is a problem that the structure becomes complicated and the installation space for the variable capacity motor is required and the layout becomes difficult. .

  In addition, there is a case where it is not desired to increase the speed of other actuators. However, in the technique disclosed in Patent Document 2, in such a case, the flow rate of the return oil is excessive, resulting in a change in speed of the other actuators. There was a problem that the operability deteriorated.

  In addition, if the technique of the said patent document 2 was applied to the turning motor, there existed a further problem in addition to the said problem. In other words, since a relief valve is usually installed at the entrance / exit port of the swing motor, when the swing operation lever is suddenly returned and sudden braking is applied during regenerative operation, the return pressure of the hydraulic oil from the swing motor is reduced to the relief pressure. As a result, the relief valve may operate. In such a case, the inertia energy at the time of deceleration is consumed as a pressure loss of the relief valve, so that there is a problem that the inertia energy that can be regenerated is reduced.

  Further, in the technique of Patent Document 3 above, regeneration is performed for a single actuator. For example, when the actuator is decelerating, the amount of hydraulic oil required for the actuator is supplied. As a result, the amount of flow that can be used for regeneration is small, resulting in almost no energy saving effect due to regeneration during deceleration.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a hydraulic control circuit for a work machine having a simple structure, excellent operability, and high energy efficiency.

  The present invention relates to a hydraulic pressure of a work machine including a variable displacement pump, a plurality of actuators that are operated by hydraulic oil supplied from the pump, a flow rate varying unit that changes a flow rate on the discharge side of the actuator, and a controller. In the control circuit, a regenerative circuit is provided which branches from an oil passage between the discharge side of the actuator and the flow rate varying means and communicates with the pump discharge side. The first control means for controlling the flow rate variable means so as to perform the regeneration by returning the hydraulic fluid on the discharge side to the pump discharge side through the regeneration circuit when the regeneration is performed. Pump through the regenerative circuit from the target pump discharge flow rate set as the sum of the supply flow rates to the plurality of actuators when not performed It is characterized in that a second control means for controlling the pump so as to reduce the flow rate of the hydraulic fluid returned to the outlet side.

  As in the second aspect of the invention, when the flow rate obtained by subtracting the flow rate of the hydraulic oil returned to the pump discharge side through the regeneration circuit from the target pump discharge flow rate is equal to or less than the minimum pump discharge flow rate, The flow rate variable means is controlled by the first control means so that the hydraulic oil on the discharge side of the actuator is returned to the pump discharge side through the regeneration circuit by a flow rate obtained by subtracting the minimum pump discharge flow rate from the target pump discharge flow rate, The second control means may control the pump so that the minimum pump discharge flow rate is achieved.

  According to a third aspect of the present invention, the apparatus includes first detection means for detecting the pressure on the discharge side of the actuator and second detection means for detecting the pump discharge pressure, and the controller is based on both detection values. It is also possible to provide estimation means for estimating the flow rate of hydraulic fluid returned to the pump discharge side through the regenerative circuit.

  According to a fourth aspect of the present invention, the work machine may be a construction machine provided with a boom lowering hydraulic cylinder as the actuator.

  According to a fifth aspect of the present invention, the work machine is a construction machine provided with a turning hydraulic motor as the actuator, and has a relief valve at each of the inlet / outlet ports of the turning hydraulic motor and a maximum return flow rate. A set pressure lower than the relief pressure when flowing into the relief valve is provided, and the controller controls the flow rate with respect to the deviation between the set pressure and the relief pressure when the return side pressure becomes higher than the set pressure. A third control unit that feedback-controls the variable unit may be provided.

  According to the present invention, when the pressure on the discharge side of the actuator is higher than the pump discharge pressure, the flow rate variable means is controlled so that regeneration is performed by returning the discharge side hydraulic fluid to the pump discharge side through the regeneration circuit. In addition, when this regeneration is performed, the pump is controlled so that the regenerative flow rate is subtracted from the target pump discharge rate that is set when regeneration is not performed. By regenerating the hydraulic oil and reducing the pump discharge amount by the regenerated flow rate, the work amount of the pump can be reduced and the energy efficiency can be improved.

  Further, according to the present invention, the actuator provided with the regenerative circuit on the discharge side regenerates deceleration energy when decelerating, and the regenerated deceleration energy is used to drive another actuator. In addition, energy can be saved even when the actuator is decelerated.

  However, for example, if the flow rate varying means is fully closed and the entire amount of hydraulic fluid on the discharge side of the actuator is allowed to flow through the regenerative circuit, the regenerative flow rate increases, and even if the pump discharge flow rate is minimized, the discharge amount may exceed. In that case, there is a problem that the pump discharge flow rate cannot be reduced by the regenerative flow rate. On the other hand, according to the second aspect of the invention, the flow rate obtained by subtracting the flow rate of the hydraulic fluid returned to the pump discharge side through the regeneration circuit from the target pump discharge flow rate set when the regeneration is not performed is the minimum pump discharge rate. When the flow rate is less than the flow rate, the flow rate variable means is controlled so that the hydraulic fluid on the discharge side of the actuator is returned to the pump discharge side through the regenerative circuit by the flow rate obtained by subtracting the minimum pump discharge flow rate from the target pump discharge flow rate. Since the pump is controlled to achieve the discharge flow rate, it is possible to reduce the work of the pump and improve the energy efficiency by regenerating the hydraulic oil on the discharge side of the actuator while ensuring the minimum pump discharge flow rate. it can.

  According to the third aspect of the present invention, the flow rate of the hydraulic fluid returned to the pump discharge side through the regenerative circuit is estimated based on the pressure detection value on the discharge side of the actuator and the pump discharge pressure detection value. The installation of a flow meter or the like is not necessary, and the configuration is simple.

  According to the fourth aspect of the invention, the potential energy when the boom is lowered is regenerated, and an energy saving effect is obtained.

  According to the fifth aspect of the invention, the flow rate passing through the relief valve is reduced, and the inertial energy consumed by the pressure loss of the relief valve is reduced. As a result, the energy that can be regenerated is increased, and an energy saving effect is obtained. .

  Hereinafter, a hydraulic excavator will be described as an example of a work machine. In hydraulic excavators, hydraulic cylinders are used as boom, arm, and bucket actuators, and hydraulic motors are used as turning actuators. Among these, especially the boom has a large potential energy when the boom is lifted, and this can be regenerated in the boom lowering operation. In addition, since the rotational inertia is large for turning, it is possible to perform energy regeneration during turning deceleration. Hereinafter, the best mode when performing each regeneration will be described.

(Embodiment 1)
FIG. 1 is an overall configuration diagram of a hydraulic control circuit of a hydraulic excavator according to Embodiment 1 of the present invention, and FIG. 2 is a functional block diagram of the controller of FIG. The first embodiment shows an example of regenerative control during the boom lowering operation.

  In FIG. 1, 7 is a variable displacement pump, 1 is a boom cylinder (corresponding to a boom lowering hydraulic cylinder) as an actuator driven by hydraulic oil supplied from the pump 7, and 2 is a bucket cylinder. 3 is a boom operation lever for the operator to operate the speed of the boom cylinder 1, and 4 is a bucket operation lever for the operator to operate the speed of the bucket cylinder 2. Reference numeral 5 denotes a boom control valve that controls the supply flow rate to the boom cylinder 1, and reference numeral 6 denotes a bucket control valve that controls the supply flow rate to the bucket cylinder 2. 8 is a controller, 9 and 10 are flow control valves, 11 to 16 are pressure sensors, 17 is a regulator of the pump 7, and 24 is a check valve.

  Among these, the flow rate adjusting valve 9 is provided on a pipe (corresponding to a regenerative circuit) 23 that further communicates a pipe 22 that connects the boom cylinder 1 and the boom control valve 5 and a discharge side pipe 21 of the pump 7. The regenerative flow rate is adjusted by changing the opening area.

  The flow rate adjusting valve 10 corresponds to a flow rate varying means and is installed between the meter-out of the boom control valve 5 and the tank 20 and controls the pressure on the discharge side of the boom cylinder 1 by changing the opening area. While functioning as an out control valve, the regenerative flow rate is adjusted in cooperation with the flow rate adjustment valve 10.

  The pressure sensor 15 corresponds to first detection means, and is provided in the pipe 22 to detect the pressure on the discharge side of the boom cylinder 1. The pressure sensor 16 corresponds to second detection means, and is provided in the pipe 21 to detect the pump discharge pressure.

  Then, the operation amount of the boom operation lever 3 is converted into a pilot pressure by the remote control valve 18 and transmitted to the boom control valve 5, and the pilot pressure detected by the pressure sensors 11 and 12 is input to the controller 8 for bucket operation. The operation amount of the lever 4 is converted into a pilot pressure by the remote control valve 19 and transmitted to the bucket control valve 6, and the pilot pressure detected by the pressure sensors 13 and 14 is input to the controller 8.

  As shown in FIG. 2, the controller 8 includes a determination unit 81, a first comparison unit 82, an estimation unit 83 and an operation unit 84 as estimation units, a first control unit 86a as a first control unit, And a second control unit 86b as two control means. Each unit 81 to 86b is configured in the controller by, for example, reading and executing various programs by a CPU (not shown). .

  Among these, the determination part 81 determines the operation direction of the boom cylinder 1 based on the detected values of the pressure sensors 11 and 12 of the pilot pressure Pi generated by the boom operation lever 3.

  The first comparison unit 82 compares the pressure Pr on the discharge side of the boom cylinder 1 detected by the pressure sensor 15 with the pressure Pp on the discharge side of the pump 7 detected by the pressure sensor 16.

  When the pressure Pr is higher than the pressure Pp as a result of the comparison by the first comparison unit 82, the estimation unit 83 determines the maximum flow rate of the hydraulic oil that flows through the regenerative circuit 23 based on both the pressures Pr and Pp (the maximum regenerative flow rate). ) Estimate Qrvmax.

  The calculation unit 84 calculates a flow rate Qp2 obtained by subtracting the maximum regenerative flow rate Qrvmax from the discharge flow rate command value of the pump 7 when regeneration is not performed (a target pump discharge flow rate set when regeneration is not performed) Qp1.

  The second comparison unit 85 compares the flow rate Qp2 with the minimum pump discharge flow rate Qpmin.

  The first control unit 86 a performs opening control of the flow control valves 9 and 10, and the second control unit 86 b performs flow control of the pump 7. That is, when the flow rate Qp2 is larger than the minimum pump discharge flow rate Qpmin as a result of the comparison by the second comparison unit 85, the second control unit 86b issues a command to the regulator 17 with the pump discharge flow rate command value as the flow rate Qp2. Then, the tilt angle of the pump 7 is controlled, and the first control means 86a performs full amount regeneration with the flow rate adjusting valve 9 fully opened and the flow rate adjusting valve 10 fully closed.

  On the other hand, when the flow rate Qp2 is smaller than the minimum pump discharge flow rate Qpmin, the second control unit 86b issues a command to the regulator 17 with the pump discharge flow rate command value as the minimum pump discharge flow rate Qpmin to set the tilt angle of the pump 7. The first control unit 86a performs partial regeneration with the opening degree of the flow rate adjustment valve 9 as Arv and the opening degree of the flow rate adjustment valve 10 as Amo. Both opening degrees Arv and Amo will be described later.

  FIG. 3 is a flowchart showing the operation of the hydraulic control circuit. Hereinafter, the operation of the hydraulic control circuit will be described.

  In FIG. 3, when the pilot pressure Pi generated by the boom operation lever 3 is detected by the pressure sensors 11 and 12 and the detected value is input to the controller 8, the determination unit 81 determines the operation direction of the boom cylinder 1 (step S1). ). Here, when the pressure Pi1 detected by the pressure sensor 12 increases to a positive pressure, the boom cylinder 1 determines that the pipe 25 side is the supply side pipe and the pipe 22 is the return side pipe.

  Next, when it is determined that the pipe 22 is a return side pipe (Yes in step S1), the first comparison unit 82 detects the return pressure detection value Pr detected by the pressure sensor 15 and the pump pressure detected by the pressure sensor 16. The detected value Pp is compared (step S2). When the return pressure detection value Pr is higher than the pump pressure detection value Pp (Yes in step S2), regenerative control described later is performed. On the other hand, when it is determined that the pipe 22 is not a return side pipe (No in Step S1), and when the return pressure detection value Pr is lower than the pump pressure detection value Pp (No in Step S2), regenerative control is performed. The process returns to step S1 without performing (step S3).

  In the regenerative control, first, the estimating unit 83 calculates the maximum regenerative flow rate Qrvmax from the maximum opening area Arvmax of the flow control valve 9 using the following equation (step S4).

Qrvmax = Cv · Arvmax · √ (2 g (Pr−Pp) / γ) (1)
Here, Cv is a flow coefficient, g is a gravitational acceleration, and γ is a density of hydraulic oil.

  Further, the calculation unit 84 obtains a flow rate Qp2 (= Qp1−Qrvmax) obtained by subtracting the maximum regenerative flow rate Qrvmax from the variable displacement pump discharge flow rate command value Qp1 when regeneration is not performed (step S5).

  The second comparison unit 85 compares the flow rate Qp2 with the minimum pump discharge flow rate Qpmin (Step S6).

  When the flow rate Qp2 exceeds the minimum pump discharge flow rate Qpmin as a result of comparison by the second comparison unit 85 (Yes in step S6), the first control unit 86a and the second control unit 86b perform the return flow rate. Full amount regeneration is performed (step S7). In this case, the second control unit 86b controls the tilt angle of the pump 7 by issuing a command to the regulator 17 with the flow rate Qp2 as a new pump discharge flow rate command value, and the first control unit 86a includes a flow control valve. 10 is fully closed, and the flow control valve 9 is controlled to be fully open. Thereafter, the process returns to step S1.

  However, if the entire discharge flow rate of the boom cylinder 1 is passed through the regenerative circuit 23 as described above, the regenerative flow rate increases, and the discharge rate may exceed even if the pump discharge flow rate is minimized. In that case, there is a problem that the pump discharge flow rate cannot be reduced by the regenerative flow rate. Therefore, if the flow rate Qp2 is equal to or lower than the minimum pump discharge flow rate Qpmin as a comparison result of the second comparison unit 85 (No in step S6), the first control unit 86a and the second control unit 86b return the return flow rate. The partial regeneration is performed (step S8). In this case, the second controller 86b issues a command to the regulator 17 with the pump discharge flow rate command value as Qmin to control the tilt angle of the pump 7, and calculates the regenerative flow rate target value Qrv = Qp1-Qmin. Next, the first control unit 86a calculates the opening area control target value Arv of the flow control valve 9 as in the following equation.

Arv = Qrv / (Cv√ (2 g (Pr−Pp) / γ)) (2)
Further, the first controller 86a obtains the opening area control target value Amo of the flow control valve 10 as follows. First, the target speed Va1 of the boom cylinder 1 is obtained from the pilot pressure detection value. The discharge flow rate Qr of the boom cylinder 1 is obtained by setting Qr = Ah · Va1 from the cylinder head side sectional area Ah and Va1.

  As a result, the flow rate of the flow control valve 10 is obtained by the following equation.

Qmo = Qr−Qrv (3)
Amo = Qmo / (Cv√ (2 g · Pr / γ)) (4)
Then, the first controller 86a controls the flow rate control valve 9 so as to become the opening area target value Arv, and controls the flow rate control valve 10 so as to become the opening area target value Amo. Thereafter, the process returns to step S1.

  By regenerating the discharge side flow rate of the boom cylinder 1 to the discharge side of the pump 7 as described above, the pump flow rate can be cut by the regenerative flow rate. For this reason, the power which drives the pump 7 can be reduced and energy saving can be aimed at.

  Further, since the pump flow rate is reduced according to the regenerative flow rate, even when the regenerative flow rate varies due to the magnitude of the load or the like, the speed of the bucket cylinder 2 is not affected by this, so that the operability can be improved.

  Further, the boom cylinder 1 provided with the pipe 23 on the discharge side regenerates deceleration energy when decelerating, and by using this regenerated deceleration energy for driving the bucket cylinder 2 different from this, the boom cylinder 1 is used. Energy can be saved even when the cylinder 1 is decelerated.

(Embodiment 2)
4 is an overall configuration diagram of a hydraulic control circuit of a hydraulic excavator according to Embodiment 2 of the present invention, and FIG. 5 is a functional block diagram of the controller of FIG. The second embodiment shows an example of regenerative control during turning deceleration.

  In FIG. 4, 37 is a variable displacement pump, 30 is a turning motor (corresponding to a turning hydraulic motor) as an actuator driven by hydraulic oil supplied from the pump 37, 31 is an arm cylinder, 32a, 32b. Is a relief valve. Reference numeral 33 denotes a turning operation lever for the operator to operate the turning operation of the turning motor 30, and 34 denotes an arm operation lever for the operator to operate the speed of the arm cylinder 31. Reference numeral 35 denotes a swing control valve that controls the supply flow rate to the swing motor 30, and reference numeral 36 denotes an arm control valve that controls the supply flow rate to the arm cylinder 31. Reference numeral 38 is a controller, 39 and 40 are flow rate adjusting valves, 41 to 46 are pressure sensors, 47 is a regulator of the pump 37, and 54 is a check valve.

  Of these, the flow rate adjusting valve 39 is on a pipe (corresponding to a regenerative circuit) 53 that further communicates a pipe 52 that communicates the meter-out of the turning control valve 35 and the tank 50 and a discharge side pipe 51 of the pump 37. A regenerative flow rate is controlled by changing the opening area.

  The flow rate adjustment valve 40 corresponds to a flow rate variable means, is installed in the pipe 52, functions as a meter-out control valve that controls the pressure on the discharge side of the swing motor 30 by changing the opening area, and the flow rate adjustment valve described above. The regenerative flow rate is controlled in cooperation with the valve 39.

  The pressure sensor 45 corresponds to first detection means, and is provided in the pipe 52 to detect the pressure on the discharge side of the turning motor 30. The pressure sensor 46 corresponds to the second detection means and is provided in the pipe 51 to detect the pump discharge pressure.

  Then, the operation amount of the turning operation lever 33 is converted into a pilot pressure by the remote control valve 48 and transmitted to the turning control valve 35, and the pilot pressure detected by the pressure sensors 41 and 42 is input to the controller 38 to operate the arm. The operation amount of the lever 34 is converted into a pilot pressure by the remote control valve 49 and transmitted to the arm control valve 36, and the pilot pressure detected by the pressure sensors 43 and 44 is input to the controller 38.

  That is, in the second embodiment, by performing the same operation as in the first embodiment, the return oil of the swing motor 30 is regenerated to the pump discharge side, and the arm cylinder 31 that is driven by the same pump as the swing motor 30 is driven, for example. Since the pump flow rate for performing the operation can be cut by the regenerative flow rate, the pump power is reduced and energy saving can be achieved.

  However, unlike the first embodiment, for example, in the case of the regenerative operation in the hydraulic excavator, when the turning operation lever 33 is suddenly returned and sudden braking is applied, the return pressure of the hydraulic oil from the turning motor 30 is the relief pressure. And the relief valve 32a may operate. In such a case, the inertia energy at the time of deceleration is consumed as a pressure loss of the relief valve 32a, so that there is a problem that the regenerative inertia energy is reduced.

  Therefore, in the second embodiment, the controller 38 includes a determination unit 81, a first comparison unit 82, an estimation unit 83 and a calculation unit 84 as estimation means, and a second comparison unit 85 similar to those in the first embodiment. In addition to the first control unit 86a as the first control unit and the second control unit 86b as the second control unit, the third comparison unit 87, the fourth comparison unit 88, and the third control unit The third control unit 89 is configured so that each unit 81 to 89 is configured in the controller by, for example, reading and executing various programs by a CPU (not shown).

  Hereinafter, the operation of the hydraulic control circuit will be described. 6 is a characteristic diagram of the relief valve in the hydraulic control circuit of FIG. 4, FIG. 7 is a flowchart showing the operation of the hydraulic control circuit, and FIG. 8 is a block diagram showing return pressure feedback control.

  As shown in FIG. 6, a target pressure Prf set so that the maximum return flow rate Qrfmax is lower than the relief pressure Prfmax when passing through the full amount relief valve 32a (or 32b) is provided.

  Then, as shown in FIG. 7, the third comparison unit 87 compares the return pressure Pr with the target pressure Prf (step S31). As a result of the comparison, if the return pressure Pr is higher than the target pressure Prf (Yes in step S31), the fourth comparison unit 88 calculates the return flow rate Qrt expressed by the following equation and the detected value of the pilot pressure. Comparison with the target return flow rate Qr is performed (step S32).

Qrt = Cv · Arv · √ (2 g (Pr−Pp) / γ) + Cv · Amo · √ (2 gPr / γ) (5)
If the return flow rate Qrt is larger than the target return flow rate Qr (Yes in step S32), the third control unit 89 performs return pressure feedback control (step S33). In other words, as shown in FIG. 8, the deviation between the return pressure Pr and the target pressure Prf is multiplied by the gain, the increment ΔAmo of the opening area of the flow rate adjustment valve 40, and each element formed by the hydraulic circuit. Return pressure Pr

  As for the control of the flow rate control valve 39, the flow rate Qp2 is calculated in the same manner as in the first embodiment. When the flow rate Qp2 is larger than the minimum pump discharge flow rate Qpmin, it is fully opened, and the flow rate Qp2 is smaller than the minimum pump discharge flow rate Qpmin. The opening area is controlled so as to be Arv obtained by the above equation (2). Thereafter, the process returns to step S31.

  In addition, when the return flow rate Qrt is smaller than the target return flow rate Qr (No in step S32), and as a result of the rapid deceleration operation, the return flow rate Qrt is decreased by reducing the turning speed of the turning motor 30, and the target return When the flow rate is equal to or less than the flow rate Qr (No in step S32), the return pressure feedback control is canceled (step S34), and the process returns to step S31.

  At this time, since the relationship between the relief flow rate and the relief pressure of the relief valve 32a (or 32b) is as shown in FIG. 6, the return pressure is controlled by this return pressure feedback control with Prf as the target value. As a result, the flow rate passing through the relief valve 32a (or 32b) decreases from Qrfmax to Qrf, and the inertial energy consumed by the pressure loss of the relief valve 32a (or 32b) decreases. As a result, the energy that can be regenerated increases, and an energy saving effect is obtained.

  In the first embodiment, the bucket cylinder 2 is illustrated as an actuator having the boom cylinder 1 and the pump 7 in common. However, an arm cylinder may be used. In the second embodiment, the arm cylinder 31 is illustrated as an actuator that shares the swing motor 30 and the pump 37. However, a bucket cylinder may be used.

  In the first embodiment, the regenerative flow rate in the regenerative circuit 23 is estimated based on the pressure detection value on the discharge side of the boom cylinder 1 and the pump discharge pressure detection value. However, the regenerative circuit 23 is provided with a flow meter. It may be measured directly. The same applies to the second embodiment.

  Further, in the first and second embodiments, the hydraulic control circuit of the hydraulic excavator is illustrated, but the hydraulic control circuit of other work machines may be used.

1 is an overall configuration diagram of a hydraulic control circuit of a hydraulic excavator in Embodiment 1 of the present invention. It is a functional block diagram of the controller of FIG. It is a flowchart which shows operation | movement of the hydraulic control circuit of FIG. It is a whole block diagram of the hydraulic control circuit of the hydraulic excavator in Embodiment 2 of this invention. It is a functional block diagram of the controller of FIG. FIG. 5 is a characteristic diagram of a relief valve in the hydraulic control circuit of FIG. 4. It is a flowchart which shows operation | movement of the hydraulic control circuit of FIG. It is a block diagram of return pressure feedback control.

Explanation of symbols

1 Boom cylinder (corresponding to actuator, boom lowering hydraulic cylinder)
2 Bucket cylinder 3 Boom operation lever 4 Bucket operation lever 5 Boom control valve 6 Bucket control valve 7 Pump 8 Controller 9 Flow rate adjustment valve 10 Flow rate adjustment valve (corresponding to flow rate variable means)
15 Pressure sensor (corresponds to first detection means)
16 Pressure sensor (corresponds to second detection means)
17 Regulator 23 Regenerative circuit 30 Swing motor (corresponds to actuator and swing hydraulic motor)
31 Arm cylinders 32a, 32b Relief valve 33 Swing operation lever 34 Arm operation lever 35 Swing control valve 36 Arm control valve 37 Pump 38 Controller 39 Flow rate adjusting valve 40 Flow rate adjusting valve (corresponding to flow rate varying means)
45 Pressure sensor (corresponds to first detection means)
46 Pressure sensor (corresponds to second detection means)
47 regulator 53 regenerative circuit 81 determination unit 82 first comparison unit 83 estimation unit (corresponding to estimation means)
84 arithmetic unit (corresponds to estimation means)
85 Second comparison unit 86a First control unit (corresponding to first control means)
86b Second control unit (corresponding to second control means)
87 3rd comparison part 88 4th comparison part 89 3rd control part (equivalent to a 3rd control means)

Claims (5)

In a hydraulic control circuit for a work machine, comprising: a variable displacement pump; a plurality of actuators that are operated by hydraulic oil supplied from the pump; a flow rate variable unit that changes a flow rate on the discharge side of the actuator; and a controller.
A regenerative circuit is provided which branches from the oil passage between the discharge side of the actuator and the flow rate variable means and communicates with the pump discharge side;
The controller controls the flow rate varying means so that when the pressure on the discharge side of the actuator is higher than the pump discharge pressure, the discharge side hydraulic oil is returned to the pump discharge side through the regeneration circuit to perform regeneration. The hydraulic oil returned to the pump discharge side through the regeneration circuit from the target pump discharge flow rate set as the sum of the supply flow rates to the plurality of actuators when the regeneration is not performed when performing the regeneration. And a second control means for controlling the pump so as to reduce the flow rate.   When the flow rate obtained by subtracting the flow rate of the hydraulic fluid returned to the pump discharge side through the regeneration circuit from the target pump discharge flow rate is equal to or less than the minimum pump discharge flow rate, the controller discharges the actuator by the first control means. The flow rate variable means is controlled to return the hydraulic fluid on the side to the pump discharge side through the regeneration circuit by a flow rate obtained by subtracting the minimum pump discharge flow rate from the target pump discharge flow rate, and the second control means controls the minimum pump discharge rate. 2. The hydraulic control circuit for a work machine according to claim 1, wherein the pump is controlled so as to have a flow rate.   First detection means for detecting the pressure on the discharge side of the actuator, and second detection means for detecting the pump discharge pressure, the controller returns to the pump discharge side through the regeneration circuit based on both detection values. The hydraulic control circuit for a work machine according to claim 1, further comprising an estimation unit configured to estimate a flow rate of the hydraulic oil to be generated.   The work machine hydraulic control circuit according to claim 1, wherein the work machine is a construction machine including a boom lowering hydraulic cylinder as the actuator.   The work machine is a construction machine having a turning hydraulic motor as the actuator, and has a relief valve at each of the inlet and outlet ports of the turning hydraulic motor, and a relief pressure when a maximum return flow rate flows to the relief valve. The controller is provided with a lower set pressure, and when the return side pressure becomes higher than the set pressure, the controller feeds back the variable flow means with respect to the deviation between the set pressure and the relief pressure. The hydraulic control circuit for a work machine according to any one of claims 1 to 3, further comprising:

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